[Rachel's Introduction: Here's video coverage (from Australia) of a very important energy development: utilities in California are building a solar energy plant to provide baseload power -- power day and night -- at prices competitive with coal. They will store solar energy as heat.]

While Australia gears up for new coal-fired power stations, the U.S. has taken a dramatic turn -- setting its sights on the sun. Two of America's biggest power companies have unveiled plans for a multi- billion dollar expansion of solar power supply. And the man behind it all is an Australian scientist who tried and failed to be heard here.

Transcript of the video:

KERRY O'BRIEN: And tonight we bring you a story that promises to strengthen the claims by supporters of solar power -- that with proper backing, it can become a viable alternative to coal-fired power; with news from the United States that two of America's biggest power utilities have unveiled plans for a multi-billion dollar expansion of solar power supply.

The company at the heart of their strategy is the one started by Australian solar expert David Mills -- the former Sydney University professor -- who left this country for California earlier this year to pursue the further development of his ground-breaking work.

What makes the announcement more significant is that the utilities are confidently predicting that their solar power will soon be providing base-load electricity -- that is, day and night -- at prices competitive with coal.

Those associated with the project believe it could signal a paradigm shift in electricity generation.

Matt Peacock reports.

MATT PEACOCK: The power of the sun. After decades as a fringe player in the energy industry, solar power is finally taking off in the world's largest economy.

VINOH KHOSLA, KHOSLA VENTURES: It's very, very exciting. There's a real sense of exuberance in belief in this new technology.

DAVID MILLS, CHAIRMAN, AUSRA INC: My hope is, my dream if you will, is that this will become a mechanism not only for the majority of the electricity generation in the United States but the majority globally.

MATT PEACOCK: As world leaders gathered in New York last week to focus on climate change, across town at the Clinton Global Initiative, giant US power companies were pledging billions of dollars of investment into solar power.

AL GORE, FORMER US VICE-PRESIDENT: We face a genuine planetary emergency, we cannot just talk about it, we have to act on it, and we have to solve it urgently.

MATT PEACOCK: For David Mills, it's vindication of a lifetime's research. Only nine months ago the former Sydney University professor was packing his bags for California's Silicon Valley, where the venture capitalist who made his fortune in IT, Vinoh Khosla, was prepared to back him.

VINOH KHOSLA: We were very excited about what they were doing and surprised at the lack of support they were getting in Australia.

MATT PEACOCK: DAVID MILLS: This is the culmination of a life's work, I've been at this for 30 years, so you can imagine how I feel. It's almost a sense of great relief that finally this problem is being noticed and action is taking place.

MATT PEACOCK: The solar technology developed by Mills already exists here in Australia -- small pilot plants attached to the Liddell coal- fired power station in the NSW Hunter Valley. Its emphasis is on simplicity. Near flat mirrors on giant hoops track the sun.

PLANT OFFICER: Sunlight, on a clear day like this, strikes those mirrors and is gathered up onto the tower, and there's an absorber underneath that tower.

MATT PEACOCK: Out comes steam, ready to drive a conventional power turbine. This is on a small scale. Mills's and Khosla's new US company, Ausra, are now planning plants far bigger.

DAVID MILLS: Our first plant size, which is still small for us, but we have to start somewhere, is about a square mile in US terms, or more than two square kilometres in the terms used in Australia, and that would generate 175 megawatts. But really we want to aim for gigawatts style plants, and they're much bigger than that.

DR MARK DIESENDORF, ENVIRONMENTAL STUDIES, NSW: It's important to get a large scale for the development to bring down costs, and the United States offers a magnificent opportunity for large-scale solar development.

MATT PEACOCK: Solar power is not new in the United States. This giant photovoltaic plant in the Mojave Desert was built during the oil shock of the 1980s. And more recent concern over global warming has led to other investment into solar thermal plants like this one in Nevada. The low cost of Ausra's new design, though, is now attracting the big money.

VINOH KHOSLA: What's very exciting is major utilities in the US are now starting to believe our story after doing their own independent due diligence. They actually believe this is competitive power generation. More importantly it's reliable power generation. We can ship them power when the sun isn't shining, which is what most utilities need.

MATT PEACOCK: The coal and nuclear industries have long asserted that base load power can't be supplied by renewable energy, a mantra repeated by our politicians.

MALCOLM TURNBULL, MINISTER, ENVIRONMENT & WATER RESOURCES : You cannot run a modern economy on wind farms and solar powers. It's a pity that you can't, but you can't.

JOHN HOWARD, PRIME MINISTER: Solar is a nice, easy soft answer. There's this vague idea in the community that solar doesn't cost anything and it can solve the problem. It can't. It can't replace base load power generation by power stations.

MATT PEACOCK: But base load power supply is just what Ausra is now being contracted to supply for the insatiable US market. It says that within two years it'll be able to economically store its hot water for more than 16 hours.

DAVID MILLS: The interesting thing is that there's a correlation between human activity [and energy use]. We get up in the morning everyday, we start using energy, we go to sleep at night. And the presence of the sun, that's natural. And that correlation means that we can get away with a lot less storage than we might have thought.

DR MARK DIESENDORF: Well, there's been a lot of nonsense talked about, in Australia and elsewhere, about renewable energy allegedly not being able to provide base load power. Not being able to substitute for coal. That's never been true. It's even untrue with regard to wind power and now with solar thermal power, it's certainly untrue.

MATT PEACOCK: the huge US investment into solar will soon make talk of clean coal and nuclear as a solution to climate change redundant, according to Mark Diesendorf at the University of New South Wales.

DR MARK DIESENDORF: Basically, the solar thermal technology will be on the ground, certainly in the United States and many other countries long before so-called clean coal and nuclear power.

VINOH KHOSLA: We think we can move much faster than nuclear and on an unsubsidised basis, we will be cheaper than nuclear power, and we should be cheaper than IGCC coal based power generation.

DAVID MILLS: In five years time, we'll have very large plants and I would say gigawatt style plants already commissioned, able to run 24 hours a day and completely replace the function of nuclear and coal plants.

MATT PEACOCK: And as international alarm mounts at the ever more obvious signs of global climate change, Mills isn't the only one who thinks the switch from fossil fuels is overdue.

DAVID MILLS: I was talking to a banker the other day and after a series of negotiations he looked at me straight and said, "I wonder if we're too late". The time has gone for easy action, that we waited too long, we've wasted 15 years but now we've got to really, really act quickly.